Spark plug and method for forming same



Feb. 9, 1960 J. L. DART SPARK PLUG AND METHOD FOR FORMING SAME Filed Jan. 7, 1957 IN VEN TOR.

A TTORNE Y United States Patent SPARK PLUG AND lgIETgOD FOR FORMING AM John L. Dart, San Diego, Calif., assignor to Qeneral M0- tors Corporation, Detroit, Mich., a corporation of Delaware Application January 7, 1957, Serial No. 632,785

Claims. (Cl. 174-152) My invention relates to spark plugs for ignition systems and more particularly to a type of spark plug which is simply and inexpensively constructed for a predetermined operating heat range and to a method for forming such plugs.

Heretofore it has been common practice in determining the heat range of a spark plug to fabricate different models of the same size plug, the insulator length and tip as well as the shell length being varied between models. Such manufacturing methods also required the availability of many different sets of tooling. It is apparent that such manufacturing methods and structural arrangements were both expensive and ineflicient by reason of the many different models required and duplication of tooling.

It is therefore an object of my invention to provide a new and improved spark plug simply and inexpensively constructed to establish a predetermined operating heat range. It is another object of my invention to provide a spark plug having a relatively short path for conducting heat away from the insulator. It is another object of my invention to provide a spark plug simply constructed to provide an efiicient heat conducting path between the insulator and the heat dissipating spark plug shell. It is another object of my invention to provide a method for forming a spark plug having a predetermined heat range.

These and other objects of my invention are made possible by providing a substantially annular-shaped bridge member formed of a relatively soft, good heat conducting material which is positioned about the tapered end of the insulator in good thermal contact with the insulator and the spark plug shell.

The objects and novel features of my invention are set forth in the foregoing description and claims taken in connection with the accompanying drawing in which Figure 1 is a view in section of a spark plug constructed in accordance with a preferred embodiment of my invention; Figure 2 is a view of the annular member forming the heat conducting bridge in the spark plug shown in Figure 1; Figure 3 is a further embodiment of the annular member shown in Figures 1 and 2; and Figure 4 is a partial sectional view with portions broken away of the lower end of the spark plug constructed in accordance with my invention and utilizing a further embodiment of the annular heat conducting member.

Referring now to Figure 1 of the drawing, there is shown a spark plug 1 comprising an insulator subassembly 3 positioned within a shell 5 in gas tight relationship therewith. The insulator 3 is formed of alumina or other suitable material in the conventional manner with an upper shoulder 7 and a lower shoulder 9, a soft metallic gasket 11, i.e., copper, being positioned on the upper shoulder 7 and a gasket 13 being provided on the lower shoulder 9 between the shoulder and an annular ledge 15 formed on the inner surface of the shell 5.

As is shown in Figures 1 and 2, the sealing gasket 13 is formed as an integral part of an annular member 17 at the upper end thereof, the upper end being flared 'ice outwardly to form a flange 18 adapted for positioning on ledge 15. Member 17 is formed of a relatively soft metal having a high coefficient of heat conductivity, such as copper. As shown, the member 17 may be generally cup-shaped in configuration with an aperture 19 formed in the bottom thereof through which the tapered firing end 21 of the insulator 3 extends. As is clearly shown in Figure 2, the side wall of the annular member 17 is generally straight, undeformed and conforming to the outline of the firing end 21 of the insulator 3 prior to initial assembly upon insulator 3. Upon installation of the member about the insulator portion 21, the lower end of the side wall is deformed to bulge outwardly and form a heat conducting annular bridge 23 having good heat conducting contact with both the inner wall surface of the shell 3 and the surface of the tapered insulator portion 21. In this manner, an eflicient and relatively short heat conducting path is provided between the insulator tapered portion 21 and the lower end of the shell 3 at the narrow annular contact area between the bridge 23 and the insulator portion 21. It should be noted that the lower end of the soft annular contact element 17 is readily bulged outwardly without placing the insulator portion 21 under undue strain because of the relatively small contact area therebetween.

The heat range of the plug is predetermined by the size of the annular heat conductingmember 17. Where a hot tip or high heat range plug is desired, the annular member 17 is relatively short in order that the heat conducting bridge 23 be positioned higher upon the insulator portion 21 and farther removed from the firing tip there of. Conversely, where a low heat range plug is desired, the side wall of the heat conducting element 17 is relatively long in order to position the outwardly bulged heat conducting bridge 23 lower down on the insulator portion 21 and closer to the firing tip thereof. As is apparent, the aperture 19 provided coaxially in the bottom of the element 17 is designed so as to be slightly smaller than the outside diameter of the insulator portion 21 at the point where the element 17 makes contact with the tapered portion 21 of the insulator. In this manner, assembly of the element 17 upon the insulator requires a small but effective amount of force in order to bulge the lower end thereof outwardly to form the bridge 23.

Figure 3 shows a modified form 25 of the element 17 wherein the lower sealing gasket 13 is not formed as an integral part of the element but is instead formed as a separate element as is used in conventional spark plug structures. Where such a modified form 25 is utilized, the lower sealing gasket 13 is, of course, assembled as a separate element between the heat conducting member 25 and the shoulder 9 of the insulator 3.

Figure 4 shows a spark plug assembly in accordance with my invention wherein the upper end of the annular member 27 is rolled over to form the lower sealing gasket 13 as an integral part thereof.

It is thus apparent that I have provided a simple and inexpensive spark plug design wherein the heat range thereof may be predetermined though utilizing the same insulator and shell merely by providing a simple bridging element having a high coefiicient of thermal conductivity and having good contact with the insulator, by reason of a press-fit therebetween, and the shell at a point which is either closer to or farther from the firing tip of the insulator and the shell depending upon whether a colder or hotter heat range is desired.

In forming the plug of my invention the insulator subassembly 3 is positioned within the shell 5 upon the ledge 15, the annular member 17 having been either assembled upon the insulator portion 21 or positioned upon the ledge 15. In either case, the tapered portion 21 is forced or pressed through the opening 19 in the bottom of member 17 until the shoulder 9 is in contact with the gasket 13, thus bulging out the lower end of the member to form a bridge 23 contacting both the shell 5 and the portion 21. Where an element of the type shown in Figure 3 is utilized, a separate gasket 13 is positioned between the flange 18 and the shoulder 9. A top gasket 11 is positioned on the upper shoulder 7 of the insulator assembly and the plug is then made gas tight by rolling the top of shell 5 over onto gasket 11 followed by Cico welding to collapse an annular portion of the shell between the shoulders in a manner well known in the art. The length of the element 17 is of a predetermined length to properly position the aperture 19 upon the insulator portion 21 for obtaining a predetermined heat range.

While I have described the novel features of my invention in terms of a preferred embodiment as shown on the drawing, other modifications thereof will be ap parent to those skilled in the art, such modifications being within the intended scope of the claims which follow.

I claim:

1. In a spark plug, the combination of a shell having a seating ledge formed on the inner wall surface thereof, an insulator subassembly positioned in gas-tight'relationship upon said ledge, said subassembly comprising an insulator having a center electrode positioned therein, said insulator having a tapered lower end portion extending below said ledge and in spaced apart relationship with the surrounding inner wall surface of said shell, and a good heat conducting annular bridging member positioned within the space between said shell and said tapered lower end portion, one end of said bridging member being in good heat conducting contact with the tapered portion of said insulator below said ledge, said bridging member extending out of contact with'said shell and said insulator from said one end to an annular portion thereof in good heat conducting contact with the inner surface of said shell adjacent said one end.

2. The combination as set forth in claim 1 wherein the other end of said annular bridging element is positioned on said ledge, said element extending below said ledge in spaced apart relationship to said insulator and said shell a predetermined distance to the point of bridging contact with said shell and said insulator for controlling the heat range of said spark plug.

3. The combination in a spark plug of a shell provided with a seating ledge, an insulator subassembly'positioned upon said ledge and having a tapered lower end portion spaced apart from said shell extending below said ledge, and a cup-shaped member having good heat conducting properties positioned about the tapered lower end portion, the upper end of said member being flared outwardly and positioned on said ledge, the bottom of said member having an aperture formed therein through which said insulator projects, the portion of said member defining the aperture being in good thermal contact with said insulator and the annular outer peripheral portion of the bottom of said member being in good thermal contact with said shell to form an annular heat conducting bridge on the lower end of said member between said shell and said insulator in a predetermined position on the insulator for controlling the heat range of said spark plug, the portion of said cup-shaped member exn tending between the outwardly flared upper end and the bottom thereof being spaced apart from both said insulator and said shell.

4. The combination as set forth in claim 3 wherein said insulator subassembly is press-fitted within the aperture.

5. In a method for forming a spark plug comprising an insulator subassembly having a tapered lower end and upper and lower shoulders and being positioned in gas-tight relationship within a shell having an annular ledge on the inner surface thereof, the steps of forcing the tapered portion of the insulator through an aperture formed in the bottom wall of an annular cup-shaped member of predetermined length to position the member about and spaced apart from the lower end of the insulator in predetermined press-fitted position thereon, simultaneously bulging the lower end of the annular member outwardly to form a bridging section on the bottom of the member, and sealing the resulting insulator subassembly within the shell with the outer surface of the bridging section in good heat conducting contact therewith at a predetermined position to controlthe heat range of the spark plug, said sealing comprising the step of positioning the lower shoulder of the insulator in gas tight relationship with the ledge of the shell.

References Cited in the file of this patent UNITED STATES PATENTS 2,047,302 Xardell July 14, 1936 2,212,725 Andres Aug. 27, 1940 2,294,249 Smulski Aug. 25, 1942 2,445,777 Hahn July 27, 1948 

